Add ffmpeg for HLS stream download support

- Add ffmpeg to Dockerfile.app for container HLS support
- Configure yt-dlp with --downloader ffmpeg --hls-use-mpegts
- Add startup health check warns if ffmpeg missing
- Update DEVELOPMENT.md with ffmpeg prerequisites and troubleshooting
- Add tests for ffmpeg HLS options and health check

src/core/providers/enhanced_provider.py

@@ -567,6 +567,9 @@ class EnhancedAniWorldLoader(Loader):
                     "socket_timeout": self.download_timeout,
                     "http_chunk_size": 1024 * 1024,  # 1MB chunks
                     "logger": self.logger,
+                    # Use ffmpeg for HLS streams and transport stream format
+                    "downloader": "ffmpeg",
+                    "hls_use_mpegts": True,
                 }
                 if headers:
                     ydl_opts['http_headers'] = headers